java - 从抽象类的子类调用 toString() 方法，会抛出 stackoverflowerror 异常

Question

在此代码中，我有一个重写的 toString() 方法。我在 ArithBinaryExpression 类的子类 AddExpression 中调用这个 toString() 方法。它向我抛出一个异常，该异常返回到 toString() 方法。我想解决这个堆栈溢出错误。任何帮助表示赞赏!

Exception in thread "main" java.lang.StackOverflowError
at main$AddExpression.toString(main.java:20)

<小时/>

  public class ArithValue implements ArithExpression {
        private double doubValue;

        ArithValue(double dVal) {
            this.doubValue = dVal;
        }

        public double result() {
            return doubValue;
        }
        @Override
        public String toString() {
            return String.valueOf(doubValue);
        }

    }



public static class AddExpression extends ArithBinaryExpression {
    public AddExpression(ArithExpression leftExp, ArithExpression rightExp) {
        super(leftExp, rightExp);
    }

    public double result() {
        double rightExp = getRightExpression().result();
        double leftExp = getLeftExpression().result();
        return rightExp + leftExp;
    }

    public String toString() {
        return "Expression: " + "(" + leftExpression.toString() + " + " + rightExpression.toString() + ")";
    }
}

<小时/>

public abstract class ArithBinaryExpression implements ArithExpression {
protected static ArithExpression leftExpression;
protected static ArithExpression rightExpression;

// constructor
public ArithBinaryExpression(ArithExpression left, ArithExpression right) {
    if (left == null) {
        leftExpression = new ArithValue(0);
    }
    else 
    leftExpression = left;

    if (right == null) {
        rightExpression = new ArithValue(0);
    }
    else
    rightExpression = right;


}
// end constructor

// accessors
public ArithExpression getLeftExpression() {
    return leftExpression;
}

public ArithExpression getRightExpression() {
    return rightExpression;
}

}

这是 ArithExpression 接口(interface):

public interface ArithExpression {
    public abstract double result();
}

Answer 1

推测:由于您对 leftExpression 和 rightExpression 使用静态变量，您的错误正在显现出来。

粘贴 main 方法可以让我们确定猜想是否正确，但这似乎是你不想要的东西